Questions and Answers
Describe the structure of a phospholipid.
A phospholipid consists of a polar (hydrophilic) phosphate group head, a glycerol molecule, and 2 non-polar (hydrophobic) fatty acid tails.
Why do phospholipids form bilayers?
They form bilayers because the polar hydrophilic group heads project outwards to be attracted to water, while the non-polar hydrophobic fatty acid tails extend inwards away from water.
The main part of a phospholipid bilayer consists of the fatty acid tails which make the plasma membrane relatively permeable to polar molecules and ions.
True
Explain Gorter and Grendel's model.
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There was no explanation of where proteins are located in the membrane in Gorter and Grendel's model.
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Explain Singer and Nicholson's model.
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Explain Davson and Danielli's sandwich model.
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What are the problems with the sandwich model?
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What did the problems with the Davson-Danielli model lead to?
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Describe the structure of plasma membranes.
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What is the function of plasma membranes at the surface of cells?
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Plasma membranes allow for cell-to-cell attachment which enables tissues to form.
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How do plasma membranes partake in cell recognition and communication?
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What is the function of plasma membranes in eukaryotic cells?
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Study Notes
Phospholipid Structure
- Composed of a hydrophilic phosphate group head, a glycerol molecule, and two hydrophobic fatty acid tails.
- Bilayer formation occurs due to the polar heads repelling water while the non-polar tails avoid it, creating an orientation ideal for cell environments.
Phospholipid Bilayer Characteristics
- Fatty acid tails primarily constitute the bilayer, granting the membrane permeability to polar molecules and ions.
Gorter and Grendel's Model
- Calculated area occupied by phospholipids in monolayer was double that of the plasma membrane, indicating a bilayer presence.
- Their methods had flaws, yet these did not undermine the conclusion that membranes are phospholipid bilayers.
Limitations of Gorter and Grendel's Model
- Failed to address the location of proteins within the membrane, highlighting a significant gap in understanding membrane structure.
Singer and Nicholson's Fluid Mosaic Model
- Established that proteins are found in various configurations: peripheral proteins on the membrane surface and integral proteins embedded within.
- Proteins appear as a mosaic due to their varied positions, with phospholipids permitting fluid movement, hence the term "fluid mosaic model."
Davson and Danielli's Sandwich Model
- Proposed a model where protein layers were adjacent to the phospholipid bilayer, creating a sandwich effect to explain substance barriers.
- High magnification electron microscopy revealed a distinct appearance supporting their model, with dark proteins and lighter phospholipids.
Critique of the Sandwich Model
- Experimental evidence, such as freeze-etched microscopy, demonstrated transmembrane proteins, contradicting the fixed-layer concept.
- Fluorescent antibody tagging showed intermixing of membrane proteins, indicating mobility rather than fixed positions.
Shift to the Fluid Mosaic Model
- Evidence gathered against the Davson-Danielli model necessitated a new understanding, leading to widespread acceptance of the Singer-Nicholson model.
Structure of Plasma Membranes
- Plasma membranes are phospholipid bilayers with a width of 7-10 nm, contributing to their thin and flexible nature.
Functions of Plasma Membranes
- Regulate molecular and ionic exchange, acting as selective barriers to polar substances.
- Facilitate cell attachment and tissue formation, enhancing structural organization within multicellular organisms.
- Participate in cell recognition and communication, crucial for tissue functionality and immune response.
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Description
Explore the key concepts of membrane structure through these flashcards. Learn about phospholipid composition and the importance of bilayer formation in cellular environments. Perfect for students looking to deepen their understanding of cell membranes.